As digital electronic products are advancing with each passing day, circuits of systems in the electronic products become more and more complex, and the problem of electromagnetic interference (EMI) or common-mode noise is then more serious, to be a significant barrier to normal operation of system.
To solve the problem of EMI, in the past, it is most common to use an electromagnetic material to achieve the suppression of EMI, in which the feature of high inductance of electromagnetic material is used to suppress the generation of EMI. However, the permeability of the electromagnetic material attenuates quickly in high frequency, in which condition makes the electromagnetic material not suitably in high-speed transmission interface with frequency section of GHz or above.
Alternatively, there is further provided with a multi-layered filter device fabricated by low/high temperature co-fired ceramics technology (LTCC/HTCC) due to recent progress in fabrication process. In spite of acceptable effect on suppression of EMI, the cost of fabrication process of LTCC/HTCC is extremely high, and the filter device is only capable of operating at low frequency range, for example, 750 MHz˜1 GHz.